In order to effectively react to, and control, the volume of traffic arising in relation to mobile radio communications networks, arrangements for achieving load-sharing between the various Radio Access Technology (RAT) networks have been introduced. These arrangements can serve to manage the distribution of data traffic between the various networks in an attempt to at least reduce the likelihood of an overload condition arising which would of course have a detrimental effect on overall system performance.
While it has proved readily possible to control such load sharing when User Equipment (UE) is in an active, or connected, state/mode, such control has not been available while the UE is in an inactive, or idle, state/mode.
However, proposals made in relation to the 3rd Generation Partnership Project (3GPP) have identified the desirability for achieving and controlling load sharing while the UE is in an inactive/idle state/mode.
As one particular example, reference is made to existing GSM/EDGE Radio Access Networks (GERAN) and UMTS Terrestrial
Radio Access Network (UTRAN) mixed networks, and in which there is currently no load sharing for UE available between those networks while the UE is in an idle mode. Indeed, the UE controlled cell reselection procedures operate quite independently of any service, or subscriber, specific considerations. Thus, if a situation should arise in which service, or subscriber, differentiation is required for traffic steering between GERAN and UTRAN, it is necessary to wait until the UE has entered a connected state/mode and in which the network controls the mobility by way of handover, or cell change, order procedures. While within the particular example of the GERAN/UTRAN environment, such an arrangement generally works well since the traffic to be steered generally comprises voice, rather than data, and the user is unlikely to notice which of the two network possibilities actually comprises the serving network. The data services, will be handled on the UTRAN since this has a higher data capacity. Thus, in the specific example discussed above of the GERAN/UTRAN mixed environment, the required load sharing is introduced primarily for voice traffic and, again with the UE in a connected state/mode, the data traffic is retained on the UTRAN side.
With regard to future developments, and the expected deployment of Evolved-UTRAN (E-UTRAN), as a capacity overlay for the UTRAN, the existing UTRAN is likely to remain utilised for data services whilst Long Term Evolution (LTE) handset usage increases. Since both E-UTRAN and UTRAN networks support relatively high speed data services, the performance differential between E-UTRAN and UTRAN is likely to be smaller than that arising between GERAN and UTRAN. In view of this, and with regard to likely future deployment of E-UTRAN, it can be seen as a potential advantage to provide for an efficient load latency arrangement for achieving packet switched data load-sharing between a UTRAN and E-UTRAN. Indeed, it has been acknowledged in relation to LTE requirements within document 3GPP 25.913 that support for load sharing and policy management across different RATs should be considered such as in particular, reselection mechanisms to direct UEs towards appropriate RATs when the UEs are in a dormant, i.e. inactive or idle, mode as well as when in an active mode/state.
This intention as illustrated in the above-mentioned 3GPP document is to ensure that LTE does not inherit the restrictions of UTRAN and that UE-controlled reselection algorithms for LTE devices can be managed by the network so that the network can move specific users from, for example, E-UTRAN to UTRAN or any other RAT when in an idle mode/state.
One known attempt to meet such a requirement was outlined in R-061238 during the 3GPP RAN2#53 meeting in Shanghai on 8-12 May 2006. This proposal was directed to the UTRAN environment and employed the Qoffsets,n parameter which is employed to bias reselection between a given pair of cells as is described further in 3GPP TS 25.304. As is known, this parameter is broadcast within the System Information Block (SIB) signalling, and in particular the SIB3 and SIB4 messages. The particular proposal relates to the addition of a UE-specific inter-RAT offset parameter which is introduced so that it can be provided to the UE by way of dedicated Radio Resource Controller (RRC) signalling. Once received, the offset value is then added, by the UE, to the particular broadcast Qoffsets,n values for all, or alternatively specific cell relations. This inter-RAT offset will apply for the duration of a timer to all, or specific, inter-RAT relationships and is also to be applied while the UE is camped on other RATs in order to prevent a ping-pong effect arising between the different RATs.
This known proposal provides for UE specific mobility between RATs by means of network-controlled cell reselection in idle mode and so there is no need for the network to push the UE into an RRC connected state in order to trigger a change of RAT for any particular UE.
It is considered however that such a known proposal exhibits limitations and inefficiencies that can lead to load-sharing performance problems.